1. Field of the Invention
The present invention relates to a resist composition, and more particularly, a resist composition that can use short wavelength light, such as that from an excimer laser for the imaging radiation, and can be developed by a basic aqueous solution following exposure. In addition, the present invention also relates to a process for forming a positive resist pattern using this resist composition, and a process for manufacturing a semiconductor device that uses the resist pattern formed using the above-mentioned process for the mask.
2. Description of Related Art
LSI and VLSI have come to be used practically in recent years accompanying the process of higher levels of integration of semiconductor integrated circuits, and the minimum line width of the wiring pattern has reached the submicron level. Consequently, it is become essential to establish hyperfine machining technologies. In the field of lithography, as a means of responding to the above requirement, ultraviolet rays as the exposure light source have been changed to far ultraviolet rays having shorter wavelengths, and at the same time, considerable research has been conducted on improvements in the exposure methods using said far ultraviolet rays as the exposure source. Accompanying this research, in the field of resist materials as well, there is a need to develop materials that combine lower absorption of light at shorter wavelengths as described above, have favorable sensitivity and have high tolerance to dry etching.
In view of these circumstances, research has been actively conducted on photolithography using a krypton fluoride excimer laser (wavelength: 248 nm, abbreviated as KrF) as a new type of exposure light source in the manufacturing process of semiconductor devices, and practical application has already begun in some areas. In addition, a resist composition using a concept referred to as chemical amplification has already been proposed by H. Ito, et al. of the IBM Corporation of the USA as a resist having high sensitivity and high resolution and being compatible with such short wavelength light sources (see, for example, J. M. J. Frechet, et al., Proc. Microcircuit Eng., 260 (1982), H. Ito, et al., Digest of Technical Papers of 1982 Symposium on VLSI Technology, 86 (1983), H. Ito, et al., "Polymers in Electronics", ACS Symposium Series 242, T. Davidson ed., ACS, 11 (1984), and U.S. Pat. No. 4,491,628). As can be easily understood from the above-mentioned references, the basic concept of this type of resist composition is to improve the apparent quantum yield by causing a catalytic reaction within the resist film to thereby increase the sensitivity and resolution of the resist composition.
In looking at the example of a chemically amplified, positive resist in which a photo acid generator (PAG), which has the effect of generating acid by light, is added to poly(t-butoxycarbonyloxystyrene) (t-BOCPVP), on which a broad range of research has been conducted thus far, at the exposed portion of the resist, protective groups in the form of t-BOC groups are deprotected by heating after exposure, namely so-called "PEB (post-exposure baking)", resulting in butene and carbon dioxide. The protonic acid formed during deprotection of t-BOC serves as a catalyst which causes the abovementioned protective group deprotection reaction to proceed along the chain, thereby resulting in a considerable change in the polarity of the exposed region. Accordingly, a resist pattern can be formed by selecting an appropriate developing solution that is able to accommodate the large change in polarity of the exposed region.
More recently, an argon fluoride excimer laser (wavelength: 193 nm, abbreviated as ArF) was expected to be used as the exposure light source for manufacturing further advanced high-integration semiconductor devices such as 1 GbitDRAM devices. This laser has a wavelength that is even shorter than the above-mentioned KrF excimer laser. However, in this deep ultraviolet wavelength region, since the aromatic rings contained in resists based on polyvinylphenol (PVP), could be used with KrF lasers, strongly absorb light at the wavelength, a pattern cannot be formed. More specifically, in the case of using, for example, a resist based on polyvinylphenol (PVP), when a fine circuit pattern of 0.2 .mu.m or less is attempted to be formed by ArF lithography, since the aromatic groups in the resist strongly absorb the ArF light during irradiation, the light is unable to reach the bottom of the resist film, thus making it difficult to form the desired resist pattern.
In order to solve the above-mentioned problems, the inventors of the present invention developed a copolymer having an alicyclic hydrocarbon group within its structure, examples of which include adamantylmethacrylate/t-butylmethacrylate copolymer and adamantylmethacrylate/3-oxocyclohexylmethacrylate copolymer, for use as the base resin of a chemically amplified resist, and a patent for said copolymer has already been filed (more specifically, see, for example, Japanese Unexamined Patent Publication (Kokai) No. 5-346668). A resist having this copolymer for its base resin has high transparency at its exposure wavelength and has excellent dry-etch resistance when an ArF laser and so forth is used for the exposure light source. However, due to its highly hydrophobic properties, it has poor adhesion to the substrate underneath, resulting in the separate problem of peeling off from the substrate during alkaline development. Thus, there is currently a pressing need to develop a resist that can be exposed in the deep ultraviolet wavelength region as in the case of an ArF laser, and has good transparency, sensitivity, resistance to dry etching and high resolution, while also exhibiting favorable adhesion to the substrate.